Active vs. Passive Magnetic Bearings

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Introduction
A magnetic bearing is a type of bearing that holds up a load using magnetic levitation. Scientists first discovered the magnetic effects in magnetic minerals in 500B.C. In the late 20th century, scientists began developing ways where this magnetic effect could be implemented into a bearing, creating magnetic bearings. Today, magnetic bearings can be found in many applications where no physical contact is required or extreme environmental conditions exists, including very high and low temperatures. Magnetic bearings also offer higher running speeds, efficiency, longer machine life and lower operating and maintenance costs due to being virtually maintenance free.
Active vs. Passive Magnetic Bearings overview
Magnetic bearings can be broken down into two different categories depending on what type of application it will be implemented in: passive magnetic bearings and active magnetic bearings. Passive magnetic bearings use permanent magnets, which allow the the shaft to hold the position through the center of the bearing without the necessary use of electrical input power. These permanent magnet are placed around the inside of the cylindrical bearing to make sure the shaft levitates freely without the help of surface friction. The advantage is that these magnets are able to keep the shaft in equilibrium without the help of external electricity. The problem that the passive magnetic bearing faces is that it is very difficult to design these types of permanent magnetic bearings because of limitations in the actual permanent magnet. The limitations are that since there is no need for external electricity in a permanent magnet, that actual lack of it makes it hard to create an assemblage of point charges that buil...

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...y of bearings is the size of the actual bearing, and the space that the bearing must fit in the specific application. This can be of conflict if you have to fit a bearing in a very small, or large location. What are the limitations of size for magnetic bearings? As of now, there is no upper bound to how large a magnetic bearing can be. However, you can run into certain design disparities when creating such large bearings. Many times, the bearing must be separated into two halves, or the magnets must be treated individually. There have also been breakthroughs in nano-technologies for bearings. These bearings are needed in the medical field, for hard drives, video heads, and optical scanners. For example, there is a micro-motor that employs a millimeter-level suspended bearing. This motor has an outside diameter of only 1.5 mm and has been run at speeds up to 600 rpm.

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